Review of the hardback: ' ... this book is thought-provoking ... distinctive approach to the twin issues of mathematical ontology and mathematical foundations'. Australasian Journal of Philosophy ...an invigorating call to foundational arms... Notre Dame Journal of Formal Logic ...this book is thought provoking...a distinctive approach to the twin issues of mathematical ontology and mathematical foundations... Australasian Journal of Philosophy ...I also think that it is one of the more philosophically significant books to have been written on this topic in some time. It provides much food for thought... this should certainly be acknowledged as an important piece of conceptual analysis, one which suggests interesting avenues for further exploration. Mary Tiles, Philosophia Mathematica ...a very lively book, filled with striking theses... The Bulletin of Symbolic Logic